1. Field of the Invention
The present invention relates to an apparatus for collecting an aggregate such as gravel and sand from the so-called returned ready-mixed concrete remaining in the tank of a concrete mixer truck which has transported a batch of ready-mixed concrete to the construction site, discharged it for placing, then returned to the concrete plant, and from the drain water discharged when washing the mixer truck.
2. Description of the Related Art
If a batch of ready-mixed concrete is transported to the construction site, and then the amount of the ready-mixed concrete is found to be insufficient during a placing operation, the placing must be interrupted until the shortage is fulfilled by a corresponding amount of ready-mixed concrete transported to the construction site for placing. The interruption of the placing operation results in a seam being formed in the concrete structure, which may have various adverse influences on the structure. For this reason, when ready-mixed concrete is to be transported, the actual practice is that an amount of ready-mixed concrete which is more than that needed is loaded on the mixer truck so that the amount of ready-mixed concrete at the construction site will not be insufficient.
As a result, in most of such actual cases, some of the ready-mixed concrete remains in the tank of the mixer truck after the required amount has been discharged from the tank at the construction site. Consequently, when the tank is washed, the drain water often contains a large amount of sand and gravel (hereinafter referred to as "sludge") which must be disposed of in a suitable place.
If the sand and the gravel are separated from the sludge, then re-used, this is advantageous in that a place for disposing the sludge is not needed. For this purpose, aggregate collecting apparatuses of various types have been proposed.
For instance, an aggregate collecting apparatus used for this purpose has a horizontal-type rotary drum the interior of which is partitioned by doughnut-shaped partition plates into three tanks, namely, a mixing and washing tank, an overflow-water transfer tank, and a trommel tank, which are sequentially arranged from the upstream side of the drum. The rotary drum is rotated at a constant speed, and sludge is charged onto the bottom of the mixing and washing tank so as to be mixed with water and washed thereby. After the mixing and washing, the sludge is scooped up from the bottom, then fed into the trommel of the trommel tank. In this tank, while the sludge is washed by fresh water being supplemented, the gravel and the sand contained in the sludge are classified and are collected. The water used in the trommel tank is allowed to flow over the partition plate between the trommel tank and the overflow-water transfer tank, thereby transferring the water to the transfer tank. Next, the water is carried by a bucket, then returned to the mixing and washing tank where the water will be used to wash newly charged sludge.
This collecting apparatus is very convenient because when sludge is charged, the gravel and the sand contained therein can be automatically separated from each other and collected.
However, since the rotary drum rotates at a speed of rotation which is constant whether the amount of sludge in the drum is large or small, the amount of sludge that can be charged in the rotary drum and processed thereby at one time is inevitably limited and cannot be increased over an upper limit. In addition, when the amount of sludge charged is small, the rotational speed of the drum can be excessively high relative to the charged amount, thereby resulting in another problem in which the sand is stirred too much to be separated, and hence, resulting in a reduction in the proportion of the sand collected.
Furthermore, clogging of the trommel cannot be prevented. In order to clean the trommel, the rotation of the trommel must be stopped, and a worker must crawl into the trommel. Thus, the work of cleaning the trommel is considerably difficult, requires a great amount of labor, and involves consumption of time.